Multi phase strip from particle and powder mixture

ABSTRACT

10:1. THE POWDER MATERIAL HAS A DIAMETER OF LESS THAN 50 MICRONS. PARTICLE SIZE AND DENSITY SEGREGATION EFFECTS ARE MINIMIZED BY ADDING POWDER TO THE PARTICLES AT A POINT IN CLOSE PROXIMITY TO THE COMPACTING MEANS. THE INVENTION IS PARTICULARLY APPLICABLE TO COPPER AND COPPER BASE ALLOYS AND IS UNIQUELY SUITED TO PRODUCE ANODE MATRIX COMBINATIONS IN ACCORDANCE WITH U.S. PAT. NO. 3,574,081.   AN ARTICLE OR STRIP FORMED BY COMPACTING COARSE METAL PARTICLES OR MIXTURE OF COARSE METAL PARTICLES AND A FINE POWDER. THE INVENTION IS PARTICULARLY DIRECTED TO THE FORMATION OF MULTI-PHASE STRIP HAVING A MATRIX FORMED OF COMPACTED COARSE METAL PARTICLES AND AT LEAST ONE SECOND PHASE FORMED OF A COMPACTED POWDER. THE APPARATUS AND PROCESS OF FORMING THE STRIP ARE ALSO PART OF THE INVENTION. THE PARTICLES HAVE A DIAMETER OF 150 TO 1200 MICRONS AND, PREFERABLY, HAVE A LENGTH-TO-DIAMETER RATIO OF 3:1 TO

Oct. 9, 1973 w, HORN ETAL MULTI-PHASE STRIP FROM PARTICLE AND POWDER MIXTURE 3 Sheets-Sheet 1 Original Filed April 26, 1971 Oct. 9, 1973 w. G. HORN AL MULTI-PHASE STRIP FROM PARTICLE AND POWDER MIXTURE Original Filed April 26, 1971 3 Sheets-Sheet 2 Oct. 9', 1973 W. G. HORN ET AL MULTI-PHASE STRIP FROM PARTICLE AND POWDER MIXTURE 3 Sheets-Sheet 3 iginal Filed April 26, 1971 3,764,308 MUL'II-PHASE STRIP FROM PARTICLE AND POWDER MIXTURE Werner G. Horn, Cheshire, and Robert M. Neumann, New Haven, Conn., assignors to Olin Corporation Original application Apr. 26, 1971, Ser. No. 137,489. Divided and this application June 16, 1972, Ser. No. 263,606

Int. Cl. 1322f 1/00, 3/18 U.S. Cl. 75-211 13 Claims ABSTRACT OF THE DISCLOSURE An article or strip formed by compacting coarse metal particles or a mixture of coarse metal particles and a fine powder. The invention is particularly directed to the formation of multi-phase strip having a matrix formed of compacted coarse metal particles and at least one second phase formed of a compacted powder. The apparatus and process of forming the strip are also part of the invention. The particles have a diameter of 150 to 1200 microns and, preferably, have a length-to-diameter ratio of 3:1 to 10:1. The powder material has a diameter of less than 50 microns. Particle size and density segregation effects are minimized by adding powder to the particles at a point in close proximity to the compacting means. The invention is particularly applicable to copper and copper base alloys and is uniquely suited to produce anode matrix combinations in accordance with U8. Pat. No. 3,574,081.

This is a division of application Ser. No. 137,489, filed Apr. 26, 1971.

BACKGROUND OF THE INVENTION This invention is directed to the formation of articles or strip by compacting coarse particles or a mixture of coarse particles and fine powder. More particularly, the invention is directed to the formation of multi-phase strip having a matrix formed of compacted coarse particles and at least one other phase formed of a compacted powder. The apparatus and process of forming the strip are also part of the invention.

It is known to form strip by hot compacting coarse particles of metals such as aluminium, magnesium, steel and nickel. It is also known to form strip by compacting powders of such metals.

However, the prior art has not compacted coarse metal particles of copper nor has it ever compacted mixtures of coarse metal particles and at least one fine powder second phase which are the essential aspects of this invention.

Strip made from metal powders or mixtures of metal powders cannot be formed at a rapid rate because of the poor flow characteristics of the metal powders. Strips made from coarse metal particles or mixtures of coarse metal particles overcome the poor flow characteristics of the fine metal powders; however, it is not possible to have a uniform dispersion of a fine second phase in the matrix because the second phase particles are very coarse.

The concept of compacting mixtures of coarse metal particles and fine powder was not considered workable because of the inherent particle size and density segregation effects due to the vast difference in size between the coarse matrix particles and the fine second phase powder.

nited States Patent 3,764,308 Patented Oct. 9, 1973 ice SUMMARY OF THE INVENTION In accordance with this invention, however, a process and apparatus has been developed wherein the powder phase or phases are added to the metal particles just before the mixture is compacted into strip. By so adding the metal powder to the metal particles, particle size and density segregation effects are substantially eliminated.

It is accordingly an object of this invention to provide multi-phase article such as strip having a matrix formed of compacted coarse metal particles and at least one second phase dispersed within the matrix formed of a fine powder.

It is a further object of this invention to provide a strip as above, wherein the matrix particles are copper or a copper base alloy.

It is a further object of this invention to provide strip formed by compacting coarse particles of copper or a copper base alloy.

It is a further object of this invention to provide an apparatus and process for compacting coarse particles of copper and copper base alloy into a densified strip.

It is a further object of this invention to provide a process and apparatus for compacting a mixture of coarse metal particles and at least one second phase comprising a fine powder into a densified article such as strip.

It is a further object of this invention to provide a process or apparatus as above wherein the coarse metal particles comprise copper or a copper base alloy.

It is a further object of this invention to provide a multiphase strip as above having improved corrosion resistance.

Other objects and advantages will become apparent to those skilled in the art from the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an apparatus suitable for carrying out the process of this invention.

FIGS. 2A, 2B, and 2C show coarse metal particles exemplary of those useful with this invention.

FIGS. 3A, and 3B show microstructures which illustrate the effect of compacting temperature when hot compacting coarse copper particles into strip.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The compacting process which must be followed in accordance with this invention when forming coarse metal particles into strip or when forming multi-phase metal strip from mixtures of coarse particles and fine powder is similar to the process of US. Pat. No. 3,076,706, granted Feb. 5, 1963. The process disclosed therein relates to a method of making a solid strip of aluminous metal from preheated coarse particles by roll compacting. The process is clearly distinguishable from the process of the instant invention since there is no suggestion of compacting mixtures of coarse metal particles and another material in the form of a fine powder to form a multi-phase strip.

US. Pat. No. 3,290,145, granted Dec. 6, 1966 and US. Pat. No. 3,413,101, granted Nov. 26, 1968 disclose the formation of multi-phase strip solely from coarse particles of aluminum and a different material or coarse particles of the different aluminum alloys. The process of these patents are also distinguishable by the absence of any suggestion of compacting mixtures of coarse metal particles and fine powders.

In accordance with the instant invention, coarse particles of a first metal are mixed with a fine powder of a second metal or other material. The mixture is then compacted to a densified strip comprising a matrix formed from the coarse metal particles and at least one highly dispersed fine second phase formed from the metal powder.

The process of the instant invention is particularly applicable to the formation of multi-phase strip in accordance with the teachings of US. Pat. No. 3,574,081, granted Apr. 6, 1971, by M. J. Pryor, assigned to the assignee of the instant invention. The process of the instant invention permits the preparation of any desired anode matrix combination as will be exemplified hereinafter.

Previously known methods of processing strip from metal powders employ relatively fine powders generally less than 50 microns in diameter. The powders are roll compacted into a green strip which is subsequently put through a multi-step sequence of sinterin and cold rollto final gage. Due to the relatively poor flow characteristics of these powders, the rolling speed is usually limted to approximately 10 feet per minute. The present invention in contrast thereto involves the compacting of coarse metal particles, preferably, elongated coarse particles mixed with at least one fine powder second phase to a fully densified strip. Due to the better flow properties of the particles, particularly, the elongated variety as compared to all powder mixtures, higher rolling speeds up to 200 feet per minute can be obtained. If the particles are preheated, no separate or additional sintering or rolling operations are necessary but they can subsequently be performed for gage or temper control or other desired purpose.

In accordance with this invention, for anode matrix combinations covered by U.S. Pat. No. 3,574,081, it is desirable to restrict interactions between the phases of the strip and, therefore, the strip is preferably processed by hot compaction without any thermal post treatment except perhaps for a flash anneal.

The process will now be described in detail with reference to FIG. 1 which shows a schematic view of a typical apparatus 1 useful for carrying out the process of this invention by the preferred method of hot compaction. A supply of metal particles 2 is held in hopper 3. The particles 2 are transferred continuously from the hopper 3 by means of vibrators G and shoot 4 into a rotary Inconel tube 5 positioned inside a furnace 6 inclined about to the horizontal. The degree of incline is not a critical aspect of this invention and may be set as desired to obtain appropriate flow rates of the particles through the furnace 6. The rotary Inconel tube 5 is rotated by conventional means such as drive means 7 connected to the motor 8.

The particles 2 during their stay in the furnace 6 and throughout the operation thereafter, until they have been compacted, are preferably maintained under a controlled gas atmosphere such as a reducing atmosphere. An atomsphere containing 96 volume percent nitrogen and 4 volume percent hydrogen has been found to be highly suitable for this purpose, and is supplied at G.

The rotation of the Inconel tube 5 causes the particles 2 to pass through the furnace '6 where they are heated to the desired temperature, preferably, above their recrystallization temperature. The particles 2 are discharged into a feeder box 9 and fall vertically into the nip of a pair of horizontally disposed rolls 10. The feeder box 9 is connected by a gas tight seal at 11 to the rotary tube 5 and is positioned above the horizontally disposed rolls 10.

To obtain more even distribution of the particles 2 over the area of the roll bite 12, a baffie 13 is preferably em ployed. The baffle 13 is generally located under the exit 14 of the rotary tube 5.

Gas burners 15 are preferably employed at the end of the rotary tube 5 which emerges from the furnace 6 to keep the particles therein from losing heat. Gas burners 16 are preferably arranged under both rolls to preheat the roll surface o a t p r tu e of 150 to 250 C. a p

4 ably, 170 to 200 C. to reduce the chilling effect of the rolls as they contact the particles.

The second phase powder 17 is preferably added to the preheated matrix particles 2 just before they enter the roll bite 12. It has been found that blending of the two components 2 and 17 at an earlier stage in the process results in severe segregation problems because of the major difference in their particle sizes. Therefore, means are provided to distribute the second phase powder 17 into the preheated matrix particles 2. The second phase powder preferably is added cold.

FIG. 1 shows one possible approach that can be used but it is not meant to be limitive of this invention.

As shown in FIG. 1, the fine powder 17 is sieve-vibrated from a container 18 located inside the feeder box 9 just above the roll bite 12. The means 19 for vibrating the container 18 is located outside the feeder box 9 and a rod 20 connected to the vibration means 19 and the powder container 1'8 transmits the necessary vibrational energy. The feed rate can be adjusted by altering the amplitude of the vibrations.

Other means for adding the second phase powders could employ spraying techniques or other known methods of distributing powders. It is merely essential that the powder be added immediately before the mixture enters the roll bite. The fully compacted strip S is guided for further processing and/or coiling by means of a ramp R.

The strip in accordance with the instant invention can be formed at speeds up to 200 feet per minute and perhaps higher; however, preferably the strip is formed between about 20 and 150 feet per minute.

The coarse particles which form the matrix phase of the composite in accordance with this invention generally have diameters of about 150 to 1200 microns and, preferably about 300 to 700 microns. Preferably, the particles have a length-to-diameter ratio of about 3:1 to 10:1 and, more preferably, about 4:1 to 6:1.

Various types of metal particles or granules which could be used in accordance with this invention are known in the art. FIG. 2 illustrates three exemplary types of copper particles which were tested for use with this invention. FIG. 2a shows a magnified view (6.5 of copper particles prepared by chopping scrap electrical wire. Since the wire was chopped in the annealed condition, the particles assume a hook type shape as shown. Most of the particles shown in FIG. 2a range between about 700 to 1200 microns in diameter.

FIG. 2b shows a magnified view (6.5x) of particles of copper formed in a manner similar to the particles of FIG. 2a; however, the particles were chopped from a finer wire and the bulk of the particles shown range between 400 and 700 microns in diameter.

FIG. 20 shows a magnified view (6.5x) of particles of electrical conductor grade copper wire of three diameters: 320 microns, 450 microns and 510 microns. The wire varied from quarter hard to spring temper and was cut to produce substantially straight particles having approximately 3. 10:1 length-to-diameter ratio.

Before proceeding further, the particles of FIG. 2 were cleaned and annealed in accordance with the practices well known in the art. These steps are not essential to the process and form no part of the instant invention. The need for cleaning and annealing is generally dependent on the prior processing of the particles. In this example the particles were soaked in benzine and rinsed in acetone to assure a surface free from any residue.

The particles were subsequently annealed for two hours at 650 C. under a reducing atmosphere to remove the surface oxides and to assure their ductility. All of the particles shown in FIG. 2 can be successfully processed into a fully densified strip.

The mechanical and electrical properties of the resulting strip as compared to wrought copper alloy strip are shown in Tab e I.

TABLE I.MECHANICAL AND ELECTRICAL PROPERTIES OF AS ROLLED STRIP Tensile properties Minimum bend Electrical radius, in. conduc- Approx. Y.S., Elong. Hardtivity,

particle 0. 1% U.T.S., percent to 90 to ness, percent Type of material temp, C. k.s.i. k.s.i. 2'' RD. R.D. Vickers ACS Copper particles Fig. 2a. 20. 7 37. 7 8. 0 4/64 008 67. 0 101 Copper particles Fig. 21)" 11.2 33. 8 44. 008 008 67. 0 101 Copper particles Fig. 2c.-- 16. 2 37. 5 36. 0 008 008 75.0 101 Annealed alloy 110 strip- 7. 5 34. 0 44. 0 008 008 62. O 101 and furher, to use substantially straight elongated par ticles because of their better flow properties. Bent particles have a stronger tendency to interlock and to accumulate in the roll bite, therefore, tending to upset the balance of the metal head required. The better flow properties of straight or slightly bent particles as in FIGS. 2b or 2c versus the hook type particles of FIG. 2a is advantageous for the attainment of higher roll speeds.

When hot compacting the particles, the temperature at which the particles are compacted into strip has been found to be a critical aspect of this invention. Preferably, the temperature should exceed the recrystallization temperature of the metal particles. FIG. 3a shows a microstructure magnified l000 of a roll compacted strip formed from out wire copper particles wherein the particles were preheated to 200 C. prior to compacting. The arrow shows the presence of a continuous oxide interface at the original particle surface. It has been found that copper strip compacted at temperatures between 200 and 250 C. exhibited very limited strength and bending capability.

FIG. 3b shows a roll compacted strip compacted at a temperature of 375 C. Note that the residual oxide interface shown by the arrow is now discontinuous with the result that the strip obtains high properties as shown in Table 1.

Therefore, in accordance with the preferred embodiment of this invention, the particles prior to compacting are heated to a room temperature in excess of their recrystallization temperature. For copper or copper base alloys, the temperature at the roll bite is 350 to 500 C. and, preferably, 375 to 450 C.

The microstructure studies in FIG. 3 show that for copper a continuous oxide film acts as a barrier to bonding and restricts recrystallization which occurs in the compacted strip. Therefore, a protective or reducing atmosphere is preferred to prevent oxide build up during the preheat cycle. A thin oxide film, however, below 300 angstroms for copper particles will break up and spherodize during compacting and will not restrict recrystallization and grain growth. The thickness of the oxide film which can be tolerated varies with particle composition.

The examples which follow illustrate the formation of multiphase strip formed by compacting preheated mixtures of coarse metal particles and a fine powder second phase. The coarse metal particles range in diameter from 300 to 1200 microns and have a length-to-diameter ratio of 3:1 to 10:1 and the fine powder second phase has a diameter less than 50 microns and preferably 1-45 microns.

Example I Copper particles having a diameter of 400 to 700 microns and a length-to-diameter ratio of 3:1 to 6:1 were employed using the apparatus of FIG. 1. The copper particles were preheated to a temperature of at least 375 C. About 0.5 weight percent of a fine aluminum powder, less than 44 microns in diameter was sieve-vibrated into the copper particles preheated to 375 C. just belore the roll bite. The compacted sheet had a clean structure with a well dispersed fine second phase. Microscopic examination did not show any interaction between the copper and aluminum resulting from the bonding operation. The resulting strip was exposed to a 3.4% sodium chloride solution which was cycled between room temperature and its boiling point for a period of one month. It was found that copper corrosion was almost entirely inhibited and the specimen was covered by a dense and evidently protective film of hydrated aluminum oxide.

Example II Iron particles about 500 microns in diameter and with a length-to-diameter ratio of 10:1 were preheated to a temperature of 500 C. and about 0.5 weight percent aluminum powder less than 44 microns in diameter was sieve-vibrated into the preheated iron particles just before the roll bite. The mixture was then compacted into a densified strip as in Example I. The resulting sample was also exposed to the sodium chloride solution as in Example I and a similar inhibition to corrosion was obtained; however, due to the smaller driving force less alumina was built up as a film on the specimen.

Example III A multi-phase copper strip was processed having a composition similar to known iron containing copper alloys. Elongated copper particles 300 microns in diameter with about a 5:1 length-to-diameter ratio were preheated to at least 400 C. Iron powder 5 microns in diameter was sieve-vibrated into the preheated copper particles in the amount of 0.5 weight percent iron and the mixture was compacted into strip as in the previous examples. The resulting strip was found to have a uniform dispersion of fine iron particles and a copper matrix similar to the known copper alloys.

Example IV Multi-phase copper strip was also prepared as in Examples I and HI with the exception that the second phase powder was graphite, lead or molybdenum disulfide having a diameter less than 50 microns. The resulting strip had a structure similar to conventionally processed material formed by casting or powder metallurgy and can be utilized in self-lubricating applications such as for bearings.

Example V Another group of copper matrix strip was prepared by adding powder less than 50 microns in diameter of alumina, barium sulfate, aluminum silicates or silicon carbide. The copper particles were microns in diameter and had about a 6:1 length-todiameter ratio. One to two volume percent of the second phase powder about 13 to 26 microns in diameter were hot compacted as in the previous examples. The resulting strips have particular use in frictional and wear resistant applications since they maintain a high coefiicient of friction and the thermal energy generated is displaced readily due to the high thermal conductivity of the matrix material.

The process of the instant invention can utilize the techniques of US. Pat. Nos. 3,533,782, granted Oct. 13, 1970 and 3,539,405, granted Nov. 10, 1970, whereby the metal particles are formed by atomizing a metal melt to form droplets which solidify into particles and the particles are compacted before they have been substantially reduced in temperature thereby eliminating an intermediate heating step.

Further, the process of the instant invention is also adapted to form composite strip comprising a backing member and a strip from particle layer as in U.S. Pat. Nos. 2,815,567, granted Dec. 10, 1957 and 3,145,560, granted July 28, 1964.

The particular settings for the roll gap will vary with the type of rolling mill employed and are conventional in the art and do not form part of the instant invention. The previous examples were carried out using a Stanat mill having 6" diameter rolls horizontally disposed. For such a mill, the roll gap settings were found to lie between .020" and .100" which yielded strip gages between 0.040" and 0.070.

The strip in accordance with this invention is preferably compacted to at least a 99.5% density.

While the examples illustrate two phase systems, it is possible by this process to incorporate a plurality of phases greater than two. The quantity of the at least one other phase is dictated by the use to which the article is to be put, but is preferably 0.1 to 20 volume percent and more preferably, 0.2 to 3 volume percent. For anode matrix combinations, such as described in U.S. Pat. No. 3,574,081, it is preferred to use 0.1 to 4.0 weight percent of the at least one other phase.

While the invention has been described with reference to the formation of strip type articles, it is equally applicable to the formation of other types of articles, such as bar, structural shapes and any other shape which is amenable to a continuous hot compacting process. The use of horizontally disposed rolls for hot compacting is not essential to this invention and any desired roll configuration or compacting means could be employed as are well known in the art. One other such compacting means which might prove suitable would be the use of a rotary swaging machine in place of the rolling mill.

The metal particles useful with this invention for forming multi-phase articles may be any of the known metals and their alloys which have the necessary ductility to be compacted into a densified article, for example, iron, aluminum, magnesium, nickel, cobalt and particularly copper.

The second phase powder may be any desired material, for example, metals, ceramics, carbides, insulators, glasses, etc. The powder need not be ductile.

While the invention has been described in detail with reference to the preferred method comprising compacting preheated particles, it is also applicable to other methods of compacting as are known in the art such as compacting followed by sintering. Further, While elongated particles are preferred in accordance with this invention because they provide the best flow properties, particles of any desired shape or mixtures with elongated particles can be used.

It is to be understood that the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are suitable of modification of form, size, arrangement of parts and details of operation. The invention rather is intended to encompass all such modifications which are within its spirit and scope as defined by the claims.

8 What is claimed is: 1. A process for forming a multi-phase article from metal particles having a diameter of 150 to 1200 microns and at least one powder material having a diameter less than 50 microns, said article consisting essentially of 0.1 to 20 volume percent of said powder and the balance being essentially said metal particles, said process comprising:

preheating said metal particles to a temperature above their recrystallization point; admixing said powder with said preheated metal particles; and

compacting said mixture to a densified article, said admixing step taking place just prior to said compacting step.

2. A process as in claim 1 wherein said powder is present in an amount from 0.1 to 4 volume percent.

3. A process as in claim 1 wherein said strip is com pacted to a density of at least 99.5%.

4. A process as in claim 1 wherein said particles substantially have a length-to-diameter ratio of 3:1 to 10:1.

5. A process as in claim 1 wherein said particles are selected from the group consisting of copper and copper base alloys, iron and iron alloys.

6. A process as in claim 4 wherein said powder is cold when it is admixed with said preheated metal particles.

7. A process as in claim 6 wherein said article comprises a strip.

8. A process as in claim 7 wherein said particles have a diameter of 300 to 700 microns and a length-to-diameter ratio of 4:1 to 6:1.

9. A process as in claim 8 wherein said powder mate rial has a diameter of 1 to 45 microns.

10. A process as in claim 5 wherein said particles are copper or copper base alloys and wherein said particles are preheated to a temperature of 350 to 500 C.

11. A process as in claim 10 wherein said powder is selected from the group consisting of iron and aluminum.

12. A process as in claim 10 wherein said powder is selected from the group consisting of graphite, lead and molybdenum disulfide.

13. A process as in claim 10 wherein said powder is selected from the group consisting of alumina, barium sulfate, aluminum silicate and silicon carbide.

References Cited UNITED STATES PATENTS 3,158,472 11/1964 Bogdandy et al. 211 3,290,145 12/1966 Daugherty 75200 3,098,723 7/1963 Micks 75DIG. 1 3,546,769 12/1970 Schwope et al 75DIG. 1 1,206,704 11/1916 Helfgott 7584 3,076,706 2/1963 Daugherty 75211 FOREIGN PATENTS 799,973 8/1958 Great Britain 75200 969,587 12/1950 France 75211 CARL D. QUARFORTH, Primary Examiner B. HUNT, Assistant Examiner U.S. Cl. X.R.

75DIG. 1, 214, 226 

